Hierarchical Bidirected Graph Convolutions for Large-Scale 3-D Point Cloud Place Recognition

In this article, we present a novel hierarchical bidirected graph convolution network (HiBi-GCN) for large-scale 3-D point cloud place recognition. Unlike place recognition methods based on 2-D images, those based on 3-D point cloud data are typically robust to substantial changes in real-world environments. However, these methods have difficulty in defining convolution for point cloud data to extract informative features. To solve this problem, we propose a new hierarchical kernel defined as a hierarchical graph structure through unsupervised clustering from the data. In particular, we pool hierarchical graphs from the fine to coarse direction using pooling edges and fuse the pooled graphs from the coarse to fine direction using fusing edges. The proposed method can, thus, learn representative features hierarchically and probabilistically; moreover, it can extract discriminative and informative global descriptors for place recognition. Experimental results demonstrate that the proposed hierarchical graph structure is more suitable for point clouds to represent real-world 3-D scenes.